This invention relates generally to washing machines, and more particularly, to methods and apparatus for controlling wash temperatures.
Washing machines typically include a cabinet that houses an outer tub for containing wash and rinse water, a perforated clothes basket within the tub, and an agitator within the basket. A drive and motor assembly is mounted underneath the stationary outer tub to rotate the basket and the agitator relative to one another, and a pump assembly pumps water from the tub to a drain to execute a wash cycle. See, for example, U.S. Pat. No. 6,029,298.
At least some known washing machines provide that an operator can select from three wash temperatures. Such machines have valve systems including hot and cold water valves. For a hot wash operation, for example, the hot water valve is turned on, i.e., opened, and for a cold wash operation, the cold valve is opened. For a warm wash, both the hot valve and cold valve are opened. The flow rates of water through the valves is selected so that the desired warm temperature is achieved using hot and cold water.
Reducing hot water usage in a washing machine facilitates reducing energy consumption by the machine during wash operations. Avoiding the use of only hot water during a hot wash, for example, would facilitate reducing the energy consumption of the washing machine. Specifically, by adding cold water for a hot wash operation, the water level required for the hot wash can be achieved and less hot water is used.
To add cold water for a hot wash operation, an additional cold water valve could be added to the valve system. The additional cold water valve for the hot wash would have a different flow rate than the cold water valve for the cold wash since less cold water would be added during a hot wash as compared to the amount of cold water added for a cold wash.
Adding an additional cold water valve for hot wash operations, however, increases the cost and complexity of the washing machine. In addition, the fill rate for a washing machine is dependent on water pressure, and water pressure can vary significantly from installation to installation. For example, if a single timed control scheme is used for adding cold water during a hot wash operation, for houses with high water pressure, too much cold water could be added during a hot wash and for houses with low water pressure, too little cold water would be added.
A temperature sensing device and a microprocessor also could be added to the system to facilitate adding cold water during a hot wash. Specifically, the temperature sensing device would be positioned to generate a signal representative of the water temperature in the tub, and the microprocessor would be coupled to the temperature sensing device and programmed to control opening and closing of the hot and cold water valves. Under control of the microprocessor, the amount of cold water flowing to the tub would be adjusted based on the temperature of the water in the tub. Adding a temperature sensing device and a microprocessor, however, increases the cost and complexity of the washing machine.